Chirping toroidicity-induced Alfvén eigenmodes (TAEs) are destabilized during neutral
beam injection on the National Spherical Torus Experiment (NSTX (Ono M. et al 2000 Nucl.
Fusion 40 557)) by super-Alfvénic ions with velocities up to five times larger than the Alfvén
velocity. TAEs exhibit repeated bursts in amplitude and down-chirps in frequency. Larger
bursts, so-called TAE avalanches, are eventually observed and correlate with a loss of fast
ions up to 30% over∼ 1 ms. Frequency, amplitude and radial structure of TAEs are …

The National Spherical Torus Experiment (NSTX,[M. Ono et al., Nucl. Fusion 40, 557
(2000)]) operates with neutral beam (NB) injection as the primary system for heating and
current drive. The resulting fast ion population is characterized by velocities up to five times
larger than the Alfvén velocity, which provides a strong drive for toroidicity-induced Alfvén
eigenmodes (TAEs). TAEs exhibit repeated bursts in amplitude and down-chirps in
frequency. Eventually, so-called TAE avalanches, which cause large (up to 30%) fast ion …